Automatic pilot



July 6, 1954 R. c. ALDERSON ET AL I AUTOMATIC PILOT Filed Dec. 17. 1951 H ELEVATOR use 26 2s i l l nm FLAP OPERATED S ERVO INVENTOR. R055 0. ALDERSON HOMER D. EGKHARDT ATTORNEY Patented July 6, 1954 UNITED STATES FATENT OFFICE AUTOMATIC ,PILOT Ross-C. Alderson, St. Louis -Park, and Homer D. it

Eckhardt; Minneapolis, :Minm,

.assignors. .tor

Minneapolis-Honeywell Regulator. Company, Minneapolis, Minn., a corp orationofDelaware Application December'li, 1951; Serial No. 262;041

(Cl. ;244P-7,7,)

1. This invention relates to -automatic pilots for an airplane wherein such airplane is provided with fiapswvhich are lotveredduring the landing operation of said airplane. Such 'fiaps, when in operated position alter the physicalrconfiguration of the craft. The operatedrflaps increase .the effective angle: of --incidence :f the wingsof the craft and also increaseitsdrag to lower the air speed to assistinlandingthe craft.

It will be appreciated-that anairplane-inflight has 'rotational inertia that resists a change :in. attitude of the airplane, for example, about-the pitch axis thereof. This airplanealso hascconventionally a horizontal stabilizer :that also' opiposes the rotation of the craft. Its damping effect depends on the airspeedof the craft.

Whenthe aircraft is provided'with an automatic "pilot that includes aidevice that detects changes in pitch attitude, it displaces .theiele-c vator" controlsurface to further; opposesuch change. The air stream impingingon the dc, fiected' surface develops arforceon the surface tending to restore the craft .to itsoriginal attitude;

When-the craft beinguthus restored hasregained momentarily its original attitude, theelevator is normally in unoperated position,: but the momentum'of the craftwculd carry it beyond the original attitude despite-the opposition stated of the horizontal stabilize-r. The craft.would then :experience'a .seriesvof oscillations about the original attitude which would beidamped out :loyv

the stabilizer.

In someautomatic pilots, a rate; of pitch ire-u' sponsive device is included which tendstosupplyh acontrol effect somewhat in advanceof the rattitude detecting device in the automatic pilot. This rate of pitch responsive device aidsthe attitude detecting device during departure-of the airplane from the original attitude-but opposes it during movement of the airplane from maximum deflection toward original attitude,

The rate of pitch device in the automaticpilct tends to apply opposite elevator asthe craft moves toward itsnormal attitude and .thusztop-r poses the inertia or momentum of the craft; The rate device in effect opposes overshoot of the craft beyond its original attitude, and thus-(has v a damping effect.

It is an object of this invention to increase the damping eifect of the automaticpilot onithe airplane when the wing flaps of the airplane pro.-. videdzwith suchautomatic pilot are in operated position wherein they increase. the effective angle of incidence and decrease the air speed .of such;

airplane.

a-irplanes automatic-pilot on the rotationiof an airplane. about the pitch axis thereof while the flaps of such airplane are inoperatedaposition.

The. above and other objects of the invention will appear hereinafter upon considerationuof theiollowing descriptionin conjunction with the accompanying drawingadisclosing .one embodiment ofsaidinven-tions Automatic pilots-for an airplane .have been heretofore provided which stabilizes the aircraft aboutv itspitch axis. The magnitude-of deviation of such aircra-ftabout. its pitch axis lfroma normal position hastbeen detectedby-ia verticalrgyroscope' which provides a control .effect proportional to the magnitude of the displacement ,from the :normal position. Such apparatus: has also included "a rate of pitch device .suchas a pitch rate gyroscope which provides .an effect in .the apparatus proportional to :the rate of Vchangelof' pitchzofsthe aircraft. The elevator controlsurfaceaisoperated in accordance with the displacementvand .rate of :change of displacement of 1 the aircraft, The relativeamount of elevator con-, trol surface displacement .tc vthe vertical gyro-.- scope displacement is oconventionally understood to determine: the pitch attitude fstiffness: of the automaticspilot. .On the otherhancl, the;.amo unt of elevator displacement .for a pitch rate gyro- 50013815851301.1883 determines. the dampingweffectof I agesignalshfrom a balanceablenetwork; The

network comprises a .plurality of voltages-generatorsewhich ;may :loez separately responsive L to the pitch iattitude and rate -'of;chang.e. of pitch attitude of .i-theaircraft. The rate of pitch attie, tude; voltas-eascnerator has-:its effecuincreased;

on the balanceable network as a flap located in 3 the wing of the aircraft is moved toward its open position wherein it decreases the air speed of the aircraft.

For an understanding of the details whereby the objects of the invention are attained reference is made to the following detailed description and accompanying drawing, the sole figure of which is a schematic arrangement of a pitch channel of an automatic pilot.

Referring to the drawing, an elevator control surface (not shown) of the aircraft is operated by conventional cables |l'l extending from a cable drum carried by an output shaft l2 of an elevator servo-motor 13. The elevator servo-motor is reversely controlled from an autopilot amplifier M. The autopilot amplifier is of the A. C. discriminator type and sheets the alternative operation of either of two relays therein depending upon the phase relationship of an alternating voltage signal with respect to an alternating voltage from a supply line. The relays in turn alternatively effect control of the direction of rotation of a reversible servo-motor. The amplifier motor combination may be such as is disclosed in Patent 2,425,734 dated August 19, 1947, to Willis H. Gille et al.

Control signals for the amplifier l4 are supplied thereto through a multiple conductor l3 from an C. to A. C. converter l5. A. C. power is supplied to amplifier |4 through conductors l1 and I8 connected to an alternating voltage source. The phase relationship of the control voltage from the conductor IS with respect to the voltage across supply conductors l1, l8 determines the direction of rotation of the elevator servo-motor |3. The D. C. to A. C. converter l may be a conventional vibrator having an operating coil connected by conductors l9 and 20 to the source of A. C. voltage. Conductor 2| extends from the vibrator to a balanceable network 23 which is the source of D. C. control voltage signals.

The balanceable network 23 comprises an elevator displacement signal generator 24, a rate of change ofpitch attitude signal generator 21, a pitch attitude signal generator 30, and a manually operable selected pitch attitude signal generator 33. Signal generator 24 comprises a potentiometer having a resistor 25 and a slider 25 cooperable therewith. Slider 26 is moved along resistor 25 in accordance with the extent of operation of elevator servo-motor |3 by a follow-up operating connection 35. Signal generator 21 comprises a potentiometer having a resistor 28 and a slider 29. Slider 29 is positioned along resistor 28 by an operating connection 33 extending from a pitch rate responsive device 31. The pitch rate responsive device 31 may be a rate gyroscope of a type (well known in the art) for detecting the rate of turn of an aircraft. Such a gyroscope has a rotor with two axes of angular freedom with its precession about one axis opposed by restraining means so that extent of precession is in accordance with the rate of pitch attitude change of the aircraft.

Signal generator 30 comprises a potentiometer having a resistor 3| and slider 32. Slider 32 is positioned along resistor 3| by a suitable operating connection 38 extending from a pitch attitude responsive device 39. The pitch attitude responsive device 39 may be a conventional vertical gyroscope whose rotor spin axis is perpendicular to the surface of the earth. The rotor is supported on its spin axis in a casing which casing in turn is carried in cross gimbals for aeeaooi rotation about two respectively perpendicular horizontal axes. Signal generator 33 comprises a potentiometer having a resistor 34 and slider 35. Slider 35 is manually adjusted along resistor 34 by a manually operable means connected thereto.

The voltage for energizing the various potentiometer resistors is obtained from a D. C. volt age source 42. The voltage source 42 may comprise a potentiometer whose resistor is connected across a suitable source of direct voltage to form a voltage divider. The resistor 43 includes a ground tap 44. The connections from the resistor 34 of potentiometer 33 to the voltage dividing resistor 43 only have been illustrated. Conductors 45 and 46 extending from the opposed ends of resistor 34 of potentiometer 33 are connected respectively to adjustable taps 41 and 48 bearing on resistor 43. Taps '41 and 48 may be adjusted relative to the ground tap 44 to select desirable positive and negative D. C. voltages relative to the voltage of the ground tap 44. The resistors of the remaining potentiometers may be similarly connected to the voltage dividing resistor 43 of the D. C. supply 42. The value of the voltages for the various ends of the potentiometer resistors relative to the voltage of the ground tap 44 are indicated adjacent thereto. The voltage of each slider in the various. potentiometers rela tive to the voltage of the ground tap 44 depends upon the relative adjustment of such slider along its resistor.

The voltage on slider 26 in signal generator 24 'is applied across a derivative network 50 consisting of a capacitor 5| and a resistor 52. To this end, a conductor 58 extends from slider 26 to one side of capacitor 5| whose opposite side is connected to one end of resistor 52 the opposite end of resistor 52 being connected to ground. The voltage between the ground end of resistor 52 and junction 51 of the capacitor 5| and resistor 52 depends upon the rate of movement of slider 26 and thus the rate of movement of the elevator servo-motor shaft |2. The voltage at junction 51 is applied through a summing resistor 53 to a network summing point 4|.

The voltage on slider 29 of signal generator 21 is applied through a summing resistor 54 to the summing point 4| of network 23.

Similarly the voltages on sliders 32 and 35 are applied through their respective summing resistors 55 and 56 to the network summing point 4|. From network summing point 4| the combined voltages are applied as stated through conductor 2| to the vibrator l5.

To increase the effect of the voltage from the aircraft pitch .rate signal generator 21 in the balanceable network 23 there is provided a second summing resistor 60 which may be placed in parallel with summing resistor 54. This parallel arrangement of the two resistors 54 and 50 is effected by a circuit closing device 5|. This circuit closing device 6| may be a single pole single throw switch the arm 55 of which may be moved to circuit closing position by an operating means 62.

The operating means 62 is adjusted by movements of a conventional wing flap 63 mounted in the wing 64 of the aircraft. The arrangement is such that when the flap 63 is in approximately its half open position the switch on 63 has completed the parallel arrangement of resistors 54 and 60 so that an increased control signal in network 23 is supplied from the pitch rate signal generator 21.

*In""operation, when the-laircra ft is in---conv'en-'-' tional flight suchels during oross=country flying; the pitch attitude gyroscope-fl sensesany change in magnitude -'of the -position of "the 'aircraf t about its 1 pitch axis to supply signals from generator 30 to relative=to the pitch axis: THe effect of any movement-"of slider 92" by*the'pitchattitude -responsive deViceNiQ depends' upon th'e voltage across'resistor '3?! the proper The voltagesselected provide sti'ifness*- ofcontrol o'f -th'e'-'elevator so that corrections are immedia-tely applied for change in pitch attitude.

The pitch attitude rate device 37 its signal generatorl'l to supply control signals in network'ti The signals from generator-'2'! reinforce th'eisignal Efrom: .generatori- '30 during deviations of the craft from normal pitch attitude until maximum deviation is attained; As the craft movesvtoward its normalposition, thesignal. .from the generator- 21 is-reversed, and. it opposes the. signal from .the,- pitch. attitude agenerator:3.0.' When the craft is verynear its-normal position after a deviation, thersignal from the pitch rate generator 21 mayexceed that from the pitch attitude generators-.30- and result :in opposite positioning of the elevator control surface. The aircraft is subjected to an opposing torque by the oppositely positioned surface so that the craft will have a tendency to reach its normal position without oscillating beyond said position.

When the pilot of such aircraft desires to land the craft, he operates the selected pitch attitude slider 35 by the operable means 40 to introduce a proper control signal. As the craft is nosed down toward the landing field, the pilot also effects by conventional means not forming a part of this invention the lowering of the wing flaps. As wing flaps are moved toward open position, flap 83 effects the operation of switch arm 65 to place resistor 69 in parallel with resistor 54.

The current through the parallel resistors 54 and 60 is greater than through the single resistor 54 and therefore the current through the other summing resistors is decreased and the voltages altered so that the voltage supplied by the signal generator 2! in network 23 is effectively increased. Thus the gain or output of the pitch rate signal generator 2! is increased during lowering of the wing flaps of the aircraft. With this increased effect or increased gain, the rate of change of pitch attitude of the aircraft exerts a greater damping effect on the movements of the aircraft about its pitch axis and has a greater tendency to damp any such oscillation.

As the flaps are moved to unoperated position, the circuit for resistor 60 is opened at the circuit closer 6! so that normal configuration of the network 23 in automatic apparatus is restored.

In conclusion, it will now be apparent that we have provided an arrangement for improving the damping effect of flight control apparatus on oscillations of an aircraft which arrangement is operative during a change in the physical configuration of the aircraft resulting from the opening of the wing flaps thereof, to thus improve the control of the craft in flight.

We claim as our invention':'

1. Control apparatus for an aircraft having an elevator control surface for positioning said craft about its pitch axis, and having wing flaps, said apparatus comprising: a motor connected to said surface and thereby adapted to position said elevator surface; balanceable voltage control means maintain -*th'e-aircraft-in a-1evelposition also adjusts con'nec'ted-to said motor means including an a'ir craft pitch rate responsive voltage providingdevice, a pitch-attitude responsive-voltage providing device, and-afollow-up voltage providing device operated from said motor; and means in said balanceable controlmeans responsive-to -opera-' tion of said-wing--flaps for increasing- -'solely the voltage from. such pitch rate voltageproviding device to saidcontrol means whereby thedamping effect of said pitch rate device and'contro'l means on-osoillationsof said aircraft about itspitch axis is increased.

2. Control apparatus for an aircraft having an elevator control-surface, for positioning -saidcraft about its pitchaxis, and'having wing flaps operable-to change the exterior physical-configuration ofsaid aircraft for decreasing the-air speed ofsaid aircraft, said apparatus comprising: a motor connected to said adapted to positionsaid elevatorsurfaoe; a balanceable control means connected to said-motor meanssaid control'means including an aircraft pitch rate gyroscope operated device, a pitchattituderesponsive device, and a-device' operated" from said motor for affecting thebalance of the control means proportional to their operation; and means in said-control means responsive-to operation of said wingflapsfor increasing-only the pitch rate gain of said pitch rate gyroscope in said control means for the same pitch rate of the craft whereby the damping effect of said control apparatus on oscillations of said aircraft about its pitch axis is increased by modifying the position of the elevator surface.

3. Control apparatus for an aircraft having an elevator control surface for positioning said craft about its pitch axis, and having wing flaps for altering the exterior physical configuration of the craft, said apparatus comprising: a motor adapted to position said elevator surface; automatic attitude condition responsive means for operating said motor for stabilizing said craft about its pitch axis said automatic means including a pitch attitude rate responsive device for damping oscillations of said craft about its pitch axis from a predetermined attitude; and means responsive to operation of said wing flaps for increasing only the damping effect of said device for the same pitch attitude rate whereby said automatic means exerts an increased effect against the oscillations of said craft about the pitch axis.

4. Control apparatus for an aircraft having an elevator control surface, for positioning said craft about its pitch axis, and wing flaps for changing the configuration of said aircraft for decreasing its air speed, said apparatus comprising: a motor adapted to position said elevator surface; means connected to said motor including a balanceable network for reversibly controlling said motor; a plurality of variable voltage signal generators in said network, one generator being operated by a gyroscope responsive to pitch axis attitude rate changes of said aircraft to provide a voltage proportional to craft pitch change rate; and means connected to said network and responsive to operation of said wing flaps for alone increasing the voltage of said gyroscope operated generator in said network to increase the craft oscillation damping characteristics of said apparatus; and means responsive to magnitude of change in pitch axis attitude for operating another signal generator in said network to provide a voltage proportional to craft surface and thereby pitch attitude change, to stabilize the attitude thereof.

5. Control apparatus for an aircraft having an elevator control surface, for positioning said craft about its pitch axis, and operable means which alter the exterior physical configuration or said aircraft, said apparatus comprising: a motor adapted to position said elevator surface; automatic craft condition rate change responsive control means connected to said motor means to efiect operation of the motor in accordance with the response of said control means for stabilizing said aircraft about its pitch axis; and means operated as said operable means are moved to operated position to alter the exterior physical configuration for varying alone the effect of said automatic control means on said motor during said condition rate change to modify the position of said elevator control surface.

6., Control apparatus for an aircraft having an elevator control surface, for positioning said craft about its pitch axis, and operable Wing flaps for altering the physical configuration of said aircraft for decreasing its air speed, said apparatus comprising: an electric motor adapted to position said elevator surface; balanceable electrical automatic control means connected to the motor and including further means for providing an electrical input signal proportional to the rate of turn of the craft about the pitch axis for controlling said motor means; followup means in said automatic control means operated by said motor for producing a control signal opposing the input signal to terminate motor operation and thereby stabilizing said aircraft about its pitch axis; and means in said control means operated as said wing flaps are moved to operated position for alone increasing the eiiect of said further means in said automatic means by increasing the electrical signal therefrom to cause said motor to modify the position of said elevator control surface.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,175,584 Zand Oct. 10, 1939 2,228,311 Gwinn, Jr Jan. 14, 1941 2,401,168 Kronenberger May 28, 1946 2,416,097 Hansen, Jr., et al. Feb. 18, 1947 2,464,629 Young Mar. 15, 1949 2,488,286 Glenny Nov. 15, 1949 2,503,346 Meredith Apr. 11, 1950 2,597,077 Douglas May 20, 1952 

